Police say all 18 potentially linked cases involve a male intruder into holiday villas occupied by British families vacationing in Portugal's Algarve region between 2004-10. Some of those incidents involved sexual assaults on children.

Madeleine was reported missing in May 2007 from her family's resort apartment in Praia da Luz on Portugal's south coast. Her disappearance remains unsolved.

Last month police said a suspect may have been responsible for 12 cases of intrusions and assaults on children in the Algarve. Police said Wednesday further inquiries have identified six more cases.